Kingdom Plantae comprises all multicellular, photosynthetic green plants from algae to angiosperms. These plants are main producers on land and in water. Green plants absorb solar energy and by using inorganic substances like C02 and water they prepare their own food material by the process of photosynthesis. In this process, they oxidize water and release oxygen. Thus they are not only the primary source of food and energy for all consumers but they also oxygenate and purify water and air. Hence they are most essential and primary biotic components of ecosystem.
Though majority of the organisms of this kingdom are photoautotrophs, some are parasites, e.g. Cuscuta. Some are insectivorous plants like Drosera, Nepenthes.
Kingdom plantae is divided into many groups like Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and Angiosperms. Cell wall made up of cellulose is a special feature of these organisms. Reserved food is carbohydrates. Life cycle has two distinct phases - gametophyte and sporophyte. Plants show different types of tissues.
They are found is various habitats such as fresh water. Sea water, deserts etc.
Major groups are:
Algae - Red, Brown and Green.
Bryophyta - Liverworts and Mosses
Pteridophyta - Ferns
Gymnosperms - Seed plants without flowers Fig. 4.4)
Angiosperms - Seed plants with flowers.
Kingdom Fungi: (multicellular Decomposers)
It is a kingdom of multicellular eukaryotic heterotrophs. All are decomposers.
They grow on decaying organic matter in moist and warm conditions. The body is made up of filamentous structures called mycelia (sing-mycelium). The mycelia are interwoven mass of thread like structure called hyphae. The cells do not contain plastids. The cell wall is generally made up of chitin, a nitrogen containing carbohydrate. Reserved food is oil and glycogen.
Vegetative reproduction takes place by fragmentation. Asexual reproduction takes place by formation of different types of spores like zoospores, conidia, sporangiospores etc. Sexual reproduction involves the fusion of similar (isogamy) and dis-similar gametes (oogamy). Spores and gametes may be flagellate or aflagellate.
Saprophytic fungi are decomposers in nature and they are responsible for maintaining the balance in the ecosystem. Parasitic fungi cause some type of disease to plants and animals. Some fungi are used in different industries like medicine, bakery etc. Yeast is an exceptional fungus as it is unicellular. Thus they resemble protists but their sexual mode of reproduction relates them to fungi. (Fig. 4.5)
Kingdom Animalia: (multicellular Consumers)
This is the kingdom of consumers. It includes all animals except the protozoans, which have been transferred to the kingdom Protista. The members of animalia are multicellular eukaryotes. The cells are without cell wall. They exhibit heterotrophic mode of nutrition. They are directly or indirectly dependent on plants. The members have well developed control and co-ordination mechanisms. This kingdom shows greater diversity as compared to the others. Locomotory organs are present. Mostly they are free living, some are parasitic and some live in association with others and lead a mutually beneficial life. Distinct embryological development is observed in all organisms, e.g. Worms, molluscs, insects, fishes, amphibians, reptiles, birds mammals etc. (Fig. 4.6)
Merits and Demerits of 5-kingdom Classification System
(1) In this classification prokaryotes are placed in a separate kingdom, Kingdom - Monera.
(2) Organisms like Euglena which possess the characters of both, plants and animals are placed in a separate group, Kingdom -Protista.
(3) As against the previous systems of classification Fungi are placed in a special group, Kingdom - Fungi
(4) The system takes into consideration phylogeny of the organisms.
(5) It is superior to 2-kingdom classification as it is based on complexity of cell structure, mode of nutrition and body organisation.
(1) Viruses are not considered in the 5-kingdom system of classification.
(2) Certain unicellular algae such as Chlamydomonas and unicellular fungi such as yeast (Saccharomyces) have disputable positions.